Methods, compositions, and automated systems for separating rare cells from fluid samples

The present invention recognizes that diagnosis and prognosis of many conditions can depend on the enrichment of rare cells from a complex fluid sample. In particular, the enrichment of fetal cells from maternal samples, such as maternal blood samples, can greatly aid in the detection of fetal abnormalities or a variety of genetic conditions. In addition, the present invention recognizes that the enrichment of rare malignant cells from patient samples, can aid in diagnosis, prognosis, and development of therapeutic modalities for patients.A first aspect of the present invention is a microfabricated filter for filtering a fluid sample. A microfabricated filter of the present invention comprises at least one tapered pore, and preferably comprises at least two tapered pores whose variation in size is 20% or less. The present invention also includes a method of enriching rare cells of a fluid sample using a microfabricated filter of the present invention.Another aspect of the invention is solutions for the selective sedimentation of red blood cells (RBCs) from a blood sample comprising a red blood cell aggregating agent and at least one specific binding member that selectively binds RBCs. Solutions of the present invention include a combined solution for rare cell enrichment that comprise RBC aggregating agents, at least one specific binding member that selectively binds RBCs, and at least one additional specific binding member for the removal of undesirable sample components other than RBCs. The invention also includes methods of using selective RBC sedimentation solutions and combined solutions for enriching rare cells of a fluid sample.Yet another aspect of the invention is an automated system for processing a fluid sample that includes: at least one filtration chamber that comprises or engages one or more microfabricated filters of the present invention; automated means for directing fluid flow through the one or more filtration chambers of the automated system, and means for collecting enriched rare cells. The present invention also includes methods of using an automated system for separating rare cells from a fluid sample. Preferred fluid samples are effusion, blood, or urine samples, and rare cells that can be enriched from such sample include nucleated red blood cells and cancer cells.